The information age has facilitated an increase in the consumer need for speed when it comes to delivering data to end-users on a DSL loop or transmission line. However, changes in the maximum DSL data rate downstream has caused some end-users to experience increased trouble or errors when their DSL data rate or sync rate is increased, for example, from 1.5 millions of bits per second (Mbps) to 3 Mbps. Research indicates that the bulk of these errors are due to transient, impulse, or non-stationary noise.
Manually handling this increase in troubled lines on a case-by-case basis does not appear to be feasible. Furthermore, a single profile that both allows the maximum data rate on the ‘non-troubled’ lines, and deals effectively with the ‘trouble’ lines has not been developed. Given the amount of variation in noise seen on some of these lines, a profile that could prevent the majority of the problems would have the effect of significantly decreasing the maximum data rate on the shortest loops. It would also have the effect of shutting down many lines that are working fine.
In many cases, DSL technology, such as asymmetric digital subscriber line (ADSL) technology, is employed today without forward error correction. This is probably a preferred way to deploy ADSL for Internet access, but as a consequence of deploying ADSL without forward error correction, the DSL loop is more subject to impulse noise. Further, at higher data rates, impulse noises are particularly acute because these higher data rates require a higher level of signal to noise ratio (SNR) which is another way of saying the DSL loops are more sensitive to lower levels of impulse noise. All transmission systems require some minimum value of SNR in order to limit a Bit Error Ratio (BER) to some acceptable level.
Impulse noise may be generated when some appliances, such as exercise machines, fluorescent lamps, and mixers, are used. When these devices are started, they can generate impulse noise with sufficient amplitude to cause an ADSL line to take errors. If enough errors are taken, the ADSL line will simply reset. Resetting is not particularly bad except that the customer may be out of service for several seconds or even minutes while the DSL line is resetting.
The problem is that many times the noise is so sporadic that it will be on long enough to cause the DSL line to reset, but then subsides while the DSL loop is reinitializing. As a result, the DSL line is reset to its original data rate. This cycle repeats itself until the noise is present during initialization. For extremely bursty noise cases, the cycle may never end.
One way to counter the problem of impulse noise is to turn on forward error correction. However, this approach is only effective when coupled with interleaving. The use of interleaving introduces delay that is problematic for Internet access. Another approach of previous systems is to slowly ramp up the data rate over a period of time, for example a month. Between each step in ramping up the data rate, there is a waiting period of several days to examine customer error rates and make the determination as to whether the error rate is such that the ramping up should cease or whether to return to a previous setting. However, this approach takes a relatively long time.
Accordingly there is an unaddressed need in the industry to address the aforementioned deficiencies and inadequacies.